Date 1 OctBand 2300 m: depth 0 cmSWE here 0 mmBasin SWE 0 mmInflow 0 m³/sReservoir 0 %FPS 0

Drag to orbit, wheel or pinch to zoom. The cut block is the snowpack of the chosen elevation band at about real size; the valley is compressed 4:1 in height. White snow cover follows the model snow line; the turquoise stream carries the basin inflow into the reservoir.

Snow Water Equivalent Basin Lab

A season from 1 October to 30 June: snow builds up in layers, warms, ripens, melts, runs off and fills a reservoir that you manage.

Weather scenario (restarts the season)

Snow surface and melt model

Water management

Snowpack layers, chosen band

Live readouts

Snow water equivalent (basin mean)

Inflow to the reservoir

Reservoir fill

Experiments

Each button runs whole seasons instantly on your device (same random weather, one change) and tabulates the water outcome.

Independent numerical checks

Controls

Drag / one finger: orbit; wheel / pinch: zoom. The three views jump to the snowpack cut, the whole basin or the reservoir.
Temperature offset and wetness restart the season (the weather is regenerated, same random numbers). Dust, slope exposure, melt model, degree-day factor, irrigation ration, pre-flood release and the band shown act at once.
"Season speed" is days per real second. The two melt models always run side by side; the button chooses which one feeds the runoff.

The science

SWE. Snow water equivalent is the depth of water the pack would give if melted: SWE = Σ ρ_k h_k / ρ_w. Fresh snow at 50-150 kg m⁻³ (here ρ_new = 50 + 1.7 (T+15)^1.5) is mostly air, so one metre of new snow holds only 5-15 cm of water. The pack is up to 6 layers, each with mass, thickness, temperature and liquid water; layers settle by viscous compaction, η = η₀ exp(0.08 ΔT + 0.021 ρ), and merge when there are too many.

Heat and cold content. Conduction through the layers: ρ c_i ∂T/∂t = ∂/∂z (k ∂T/∂z) with k = 2.22 (ρ/1000)^1.88 W m⁻¹ K⁻¹, solved implicitly (tridiagonal) so any time step is stable. Cold content CC = Σ m c_i (0 − T) must be warmed away (ripening) before meltwater can leave the pack; water that meets a cold layer refreezes and releases L_f = 3.34×10⁵ J/kg. Each layer holds up to 5 % liquid water by mass and passes the rest down.

Melt. Energy balance: Q = (1 − α) S + h (T_a − 0) + Q_rain, melt = (Q − G) Δt / L_f, where G is heat conducted into the cold pack, h = 10 W m⁻² K⁻¹ is a bulk longwave + turbulent coefficient and α decays from 0.85 to 0.45 as the surface ages (dust lowers the maximum). Degree-day: M = DDF · max(T_a, 0), DDF about 5 mm °C⁻¹ day⁻¹. Both run side by side.

Basin and reservoir. Five 300 m elevation bands (1700-2900 m) with lapse rate 6.5 K/km and precipitation +5 % per 100 m. Runoff feeds a fast store (K = 30 h) and a slow store (K = 20 d) with exact exponential updates; a small evapotranspiration loss comes from the slow store. Reservoir: dV/dt = Q_in − Q_release − E − Q_spill.

Honest limits. One synthetic weather series at a 1500 m station, not a forecast or any real catchment; 1-D layers (no wind drift, no avalanches, no basal ice, no sublimation); the constants (compaction, retention, h, DDF, demands) are illustrative model values; the cut-away uses a compressed 4:1 valley and decorative crystal shapes. Assets built with Blender; scene by Three.js.